1. Field of the Invention
The present invention relates to a stand-up type personal watercraft which is operated by an operator riding in a standing position on a foot deck of a rear portion of a body of the watercraft.
2. Description of the Related Art
In recent years, jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is equipped with an engine mounted within a space surrounded by a hull and a deck. The engine is configured to drive a water jet pump, which pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of the hull and ejects it rearward from an outlet port of the water jet pump. As the resulting reaction, the personal watercraft is propelled forward.
There is a straddle-type personal watercraft operated by an operator straddling a seat mounted over an upper portion of a body of the watercraft and a stand-up type personal watercraft operated by an operator standing on a foot deck provided on a rear portion of the body. In recent years, in the straddle-type personal watercraft, the use of a four-cycle engine in place of the conventional two-cycle engine has been contemplated (Japanese Utility Model Publication No. Hei. 5-40262). And, a need for the four-cycle engine in place of the two-cycle engine also exists in the stand-up type personal watercraft. However, if the four-cycle engine is mounted in the stand-up type personal watercraft, the following problems will arise.
Since the four-cycle engine is constructed such that valve drive components such as air-intake and exhaust valves and a cam are provided above a cylinder, the four-cycle engine generally has a height larger than that of the two-cycle engine. Therefore, it is necessary to mount the four-cycle engine that is larger in size than the two-cycle engine in a space of the body of the stand-up type personal watercraft, which is smaller than that of the straddle-type personal watercraft.
Since the four-cycle engine includes the valve drive components within a cylinder head as described above and hence its center of gravity is located higher, the center of gravity of the personal watercraft equipped with the engine tends to be located higher. Since the body of the stand-up type personal watercraft has a relatively small width, the watercraft easily rolls. Therefore, it is necessary to locate the center of gravity of the components, including the engine and auxiliary devices as low as possible.
In addition to the center of gravity, attitude (balance) of the watercraft affects cruising capability. The attitude of the watercraft is determined by weight associated with the components, such as the engine and the auxiliary devices and the operator, a buoyant force, and arrangement or placement of these components and the operator.
In the stand-up type personal watercraft equipped with the two-cycle engine, since the components mounted within the body have a relatively small weight, the arrangement of the component does not substantially affect the attitude of the personal watercraft. Instead, because of the small-sized body, weight and attitude of the riding operator significantly affect the cruising attitude of the watercraft. Therefore, the two-cycle engine is typically mounted in the stand-up type personal watercraft such that it is located forward of a center position in the longitudinal direction of the body, considering the condition in which the operator rides on the foot deck provided on the rear portion of the body.
In the case of the four-cycle engine, on the other hand, since the total weight of the components mounted within the body, including the engine, is relatively large, the weight and position of the riding operator affects less than those in the case of the two-cycle engine. In other words, the center of gravity of the body containing the components is important, and it is therefore necessary to properly arrange the components so that the weight and the buoyant force are well balanced.
Within the body of the personal watercraft, an oil tank is equipped to reserve oil for lubricating the engine. Since the stand-up type watercraft is small and lightweight in contrast to the straddle-type personal watercraft, the body varies its attitude according to an operation performed by the operator. For example, during cruising, the body frequently turns at a sharp angle. When the watercraft turns at a sharp angle, a lateral great inertia force is applied to the body. In the case of a horizontally elongate oil tank used in the conventional two-cycle engine, such great inertia force causes oil contained therein to undesirably gather at one side.
In order for the watercraft to skip along the surface of choppy water, the hull of the watercraft is typically shaped such that a front portion protrudes slightly downward and an inner surface of an engine-mounted portion of the hull is inclined forwardly downward. This makes an inner bottom surface of a crankcase of the engine inclined forwardly downward. Therefore, an oil-collecting structure that collects oil reserved in a bottom portion of the crankcase is typically located at a front portion within the crankcase.
However, in the stand-up type personal watercraft, when the operator rides on the foot deck at the rear portion of the body, its fore part is located higher than its aft part. When the watercraft starts cruising, the fore part is located higher than the fore part before cruising. In this case, the inner bottom surface of the crankcase is inclined such that its front portion is located higher than its rear portion and an inertia force is generated rearward while the body is accelerating forward. Under this condition, the oil gathers in the rear portion the inner bottom portion of the crankcase. As a result, the oil is not collected efficiently from a front portion of the crankcase.